Gear systems for wind turbines require lubrication during normal operation. For efficiency reasons it is sometimes desirable to provide lubrication to the gear system by means of a circulation system circulating a minimum amount of lubricant in such a manner that only an amount of lubricant necessary for lubricating the gear system during operation is present in the gear system at any time during normal operation. However, this has the disadvantage that in the case of an emergency, possibly causing the gear system to slow down or even stop, the gear system is left with insufficient lubrication. It has previously been attempted to address this problem.
GB 2 201 200 discloses a method of lubricating gear means for a wind energy installation. The method comprises the steps of maintaining operational lubrication by an oil-circulating system with injection lubrication, with the oil being cooled at the same time. The normal height of the oil level in the gear means casing is increased to a height necessary for splash lubrication when the rotational speed of the gear means falls below a settable value. To increase the height of the oil level, an additional quantity of oil is fed to the casing from a reservoir.
In the method disclosed in GB 2 201 200 it is necessary to measure the rotational speed of the gear means in order to detect that a situation is occurring which requires a higher oil level, and the reliability of the method is thereby dependent on the reliability of a sensor used for measuring the rotational speed. Furthermore, it is not possible to reduce the response time of the system below a value defined by the time it takes to detect the rotational speed, compare the detected rotational speed to a threshold value, determine that the threshold value has been exceeded and initiate increasing of the oil level. Thus, the system has an inherent inertia.